1. Field of the Invention
The present invention relates generally to nonwoven composite materials and their methods of manufacture and, more particularly, to nonwoven fibrous panels adapted for thermoforming. Specifically, the present invention relates to nonwoven moldable composite materials having enhanced stiffness/weight ratios and enhanced resistance to shrinkage during thermoforming and their methods of manufacture.
2. Description of the Prior Art
Nonwoven needlepunch fiber technology has been utilized in the past in a variety of manners to form a diverse number of nonwoven flexible fabric materials and products. Examples of such technology for producing flexible nonwoven materials include U.S. Pat. Nos. 4,420,167, 4,258,094, 4,581,272, 4,668,562, 4,195,112, 4,342,813, 4,324,752, 4,315,965, 4,780,359, and 5,077,874.
In certain applications, however, flexible nonwoven materials having fabric-like surfaces are not the most desired product. In fact, there are certain instances where a more rigid nonwoven material is desirable, for example for use as a trunkliner to protect electronic components located in the trunk area. In certain past situations, plastics have been utilized for such applications. Historically, plastic composite panels have been manufactured using any number of different techniques. In the case of panels or materials suitable for low pressure thermoforming, which is desirable for trunkliner applications and other similar type of applications requiring molding, several processes have been utilized.
One typical process of the prior art is based on paper making technology. In this instance, short staple fiber reinforcement materials, having fiber lengths typically less than one inch, are mixed with a desired resin system, dispersed in a slurry, applied onto a porous belt, dried, and then consolidated using heat and pressure. In this instance, the desired resin system has been either a resin emulsion or additional fibrous materials of a lower melting point.
Other prior art processes rely on extrusion techniques to form a melt of the desired resin, which may or may not contain short staple fiber reinforcement materials and/or fillers. Panels are then formed by directing the molten resin through a slot die. One variation of this process uses a resin sheet which is combined with premanufactured reinforcement webs shortly after the extrusion die. These materials may be made in a sandwiched construction of resin-reinforcement-resin, and then consolidated through a compression operation consisting of high pressure rollers or presses.
In yet another prior art process, which has been used extensively for light weight textile type products such as diaper linings, interlinings, and the like, includes forming a nonwoven structure through a textile process such as carding or airlay technology of primarily reinforcement fibers. These reinforcement fibers can contain lower melting binder fibers. This nonwoven structure is then exposed to heat and pressure to form a fibrous nonwoven structure containing bond points in the structure. This is not unlike flexible textile manufacturing processes described in some of the aforementioned patents. Alternatively, the nonwoven structure may be exposed to resin systems via a spray or dip application of resin emulsions, which are then dried by way of heat and/or pressure.
Some of the drawbacks of the textile based technology discussed above, however, include the fact that if additional decorative or reinforcement materials such as carpeting or the like needs to be adhered or connected to the composite substrate material, such additional material has traditionally been needlepunched to attach it to the composite materials already formed. Such needlepunching has been shown to change the appearance of the decorative material or weaken the reinforcement materials. In the alternative, such carpeting or other decorative layer can be separately adhered to the composite substrate by use of separate adhesive applications.
Moreover, such composite materials of the past have exhibited a certain amount of shrinkage when subsequently exposed to additional heat during thermoforming processes to mold the composite into a desired shape for application as a trunkliner, dash panel or any other type of part. Such shrinkage during thermoforming can cause missizing of the desired component part. Alternatively, it requires precise prediction with respect to the amount of shrinkage in order to incorporate such shrinkage into the original panel size prior to thermoforming. Yet another alternative includes oversizing the panel so as to insure that shrinkage occurring through thermoforming would not affect the desired end product size. However, excess material must be trimmed off, and this is unnecessary waste. Therefore, there remains a need for a stiff, less flexible nonwoven composite material which is capable of being thermoformed and molded without shrinkage as well as providing alternate attachment mechanisms for decorative or reinforcement materials.